1. Field of Invention
This invention belongs to the filed of methods of computer simulation based control of laser deposition of material on a similar or dissimilar substrate via delivery into the high energy beam (laser, electron-beam, etc.) in the form of powder or wire, melting in the beam and fusing the molten deposit to the substrate.
1. Prior Art
Material deposition utilizing a focused energy beam (e-beam or laser) is a rapidly emerging technology, which allows manufacturing of near-net to net-shaped structural metal parts, improvement of the performance by modification of part surface, and repair of damaged part. This technology supplements traditional technologies (casting, molding, sintering, etc.) providing additional benefits such as very low or no porosity, higher uniformity of material composition and microstructure, higher flexibility (low retooling time), and higher portability of hardware. Additionally, high energy beam assisted material deposition allows manufacturing of functionally graded materials and complex geometries, which are impossible to produce by other technologies. Because of this great potential, high energy beam material deposition is a crucial technology for many industries including aero-space, transportation, and metal fabrication.
Initially, laser and e-beam cladding, a simplest type of high energy beam assisted material deposition, was commercialized and implemented. Laser and e-beam cladding technology is utilized to repair rails (Duroc AB, Sweden), repair turbine blades (Huffman Corporation, USA), improve surface of automobile parts (Caterpillar, USA), and in many other applications.
The major implementation problem was to select processing parameters producing deposition without defect known as xe2x80x9clack of fusionxe2x80x9d, i.e. incomplete melting of the deposited material and joining to the substrate. In order to facilitate the selection of the process parameters providing free of lack of fusion cladding several computer models [1,2] were developed. The utilization of these models to facilitate cladding process development in GE Aircraft Engines proved to be unsuccessful [3]. The models [1,2] were based on approximate and incorrect physical concepts providing accuracy of prediction insufficient for practical needs. Therefore, the laser and electron beam cladding process parameters selection is performed empirically via trial and error method. The specifics of cladding are such that this technology is feasible for commercialization, although empirical selection of the processing conditions increases cost of the technology.
Multiple attempts to commercialize another type of high energy beam assisted material deposition, called free forming or near net shaping, demonstrated that industrial implementation is unfeasible without utilization of process modeling. This is determined by several factors. First, unlike in case of cladding, in free forming the geometry of the substrate is constantly changing. Therefore, in order to empirically select processing parameters providing deposition without lack of fusion defect, the experiments must be performed on the substrates with geometry reproducing the real part. Experience shows that the cost of such development work makes application of the technology unfeasible. Second, in majority of applications of free forming, such as aerospace industry, the microstructure of the deposited part is important. The microstructure is determined by the thermal history of the part. The experience shows that it is impractical to search for the parameters providing desired microstructure via empirical trial and error method. Third, in case of deposition of multiple materials in order to create graded chemical composition in the manufactured part, the evaporation can significantly influence the chemical composition of deposit, such that it will differ from the simple algebraic sum of the component materials supplied in the beam by powder or wire. The empirical way of determining the processing parameters, which provide desired change of chemical composition of the deposit is impractical.
The presented invention provides a means allowing control of high energy beam assisted material deposition based on the computer simulation of the process. The process control via numerical simulation is obtained by:
1) defining the processing parameters resulting in the optimal shape of molten zone allowing complete fusion of the deposited material to the substrate,
2) predicting shape of the deposit (shape of the cross section or height and width) which allows planning of the deposition path by CAD software
3) predicting the contour of the melt puddle edge and the surface temperature distribution at any stage of the fabrication, such allowing intelligent implementation of multiple monitoring techniques suggested for the material deposition.
This invention includes the method for simulation of laser processing regimes in which material is deposited on the surface in form of fused layer. The method includes utilization of the unique physical model representing all main physical processes taking place during laser assisted material deposition, corresponding mathematical model consisting of equations describing the relevant physical processes, and a computer code used for numerical calculations of the parameters of interest according to the mathematical model.